The Octopus gem allows you to do Database Sharding in ActiveRecord and they just released version 0.6.0.

A couple of different things are new in this version, like some refactorings and clean ups, removal of the Octopus::Logger, using the MySQL2 Driver instead of MySQL for the spec suite and, most importantly dropping support for Rails 2.x.

If you need Rails 2, then Octopus 0.5 is the latest version that you can use. Octopus 0.6 is Rails 3 only and the not­-yet-­released Octopus 0.7 is planning to support Rails 4.